Transport refrigeration systems are commonly used to transport perishable cargo, such as, for example, produce, dairy products, cut flowers, and frozen products, such as meat, poultry, and fish. Transport refrigeration systems may include refrigerated trailers, trucks, containers, and railroad cars, for example. In the case of refrigerated trucks, a transport refrigeration system may typically be mounted to the truck, typically behind the truck or on the roof of the truck for maintaining a controlled temperature environment within the cargo space within the truck. In the case of refrigerated trailers, which are typically pulled behind a tractor cab, a transport refrigeration system may typically be mounted to the trailer, typically to the front wall of the trailer for maintaining a controlled temperature environment within the cargo space within the trailer. In the case of refrigerated containers, a transport refrigeration system may typically be mounted to one end of a container box.
Conventionally, transport refrigeration systems used in connection with refrigerated trucks and refrigerated trailers and refrigerated containers include a transport refrigeration unit having a refrigerant compressor, a condenser comprising a condenser coil with one or more associated condenser fans, an expansion device, and an evaporator comprising an evaporator coil with one or more associated evaporator fans, which are connected via appropriate refrigerant lines in a closed refrigerant flow circuit. The compressor and other components may typically be powered by a diesel engine and/or an electric motor. Air or an air/gas mixture or other gas is drawn from the interior volume of the trailer by means of the evaporator fan(s) associated with the evaporator, passed through the airside of the evaporator in heat exchange relationship with refrigerant whereby the refrigerant absorbs heat from the air, thereby cooling the air. The cooled air is then supplied back to the cargo space.
In conventional practice, a transport refrigeration unit installed on a refrigerated truck or trailer may operate in different control modes, such as a temperature pulldown mode, a temperature control mode, or an idle mode. In a typical temperature pulldown mode, the refrigerant compressor, the condenser fan(s) and the evaporator fan(s) are operating with the refrigerant compressor generally operating at full capacity to lower the temperature within the cargo space to a desired set point temperature appropriate for the particular cargo stowed in the cargo space. In a typical temperature control mode, the refrigerant compressor, the condenser fan(s) and the evaporator fan(s) are still operating, but the refrigerant compressor may be operating at a significantly lower capacity so as to maintain the temperature in the cargo space within a specified range of the desired set point temperature and avoid over cooling. In the temperature control mode, heaters associated with the evaporator may also be activated as necessary to warm the air passed through the evaporators by the evaporator fan(s) to prevent over cooling. In the idle mode, the refrigerant compressor and the condenser and evaporator fans are off.
There has been ongoing interest in more advanced control modes to provide for more complex temperature control purposes. For example, U.S. Pat. No. 5,163,301 discloses a refrigeration system control with an illustrative object to provide an improved means for controlling the temperature of chilled air delivered to a refrigerated container unit when operating under light load conditions. As another example, U.S. patent application publication number 2008/0289354 discloses a method for creating multiple refrigerated compartment spaces having precision temperature control, which includes prioritizing the compartments by identifying at least one priority compartment to be held at a setpoint temperature, and limiting refrigerant flow to all but the priority compartment when there is insufficient cooling capacity to maintain all compartments at their respective setpoint temperatures. Additionally, there has been significant interest in providing for economy modes that manage the energy expenditure of transport refrigeration units.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.